Particle form evaporation is described in U.S. Pat. Nos. 4,310,973 and 4,263,091 and in two U.S. patent applications (Ser. Nos. 426,433 and 427,220) filed on the same day as the parent of this application. W. R. King is named as the sole inventor in one application. W. R. King and R. E. Elliott are the co-inventors named in the other application. The above-identified patents and applications are incorporated by reference herein. The reader is encouraged to consult and study these sources of information to facilitate a comprehensive and thorough understanding of my present invention.
In brief summary particle form evaporation involves the evaporation of solvent or liquid from a polymer. This is accomplished by introducing a polymer-containing solution or a mixture of polymer and liquid into an agitated bed of hot polymer particles. The hot agitated bed, typically contained in a cylindrical vessel, facilitates evaporation of solvent or liquid. The introduced polymer upon agitation and drying assumes a particle form and replaces other dry polymer particles in the bed which are removed as the product of the process.
Agitation is typically accomplished by positioning within the vessel containing the polymer particle bed a mechanical agitation means such as, for example, rotating mixer blades. The term blade is intended to be broadly construed and includes, for example, paddles, rods, pins, etc. Agitation of the bed causes an input of energy into the system which heats the polymer particles. For good results the bed should be heated to a temperature of at least about the boiling point of the solvent or liquid. The heat can be supplied by agitation alone or in combination with other sources of heat such as, for example, a hot gas directed through the bed or a heating jacket positioned around the bed.
The feed (polymer solution or polymer-liquid mixture) can be introduced into the bed in any of many ways. For example the feed can be sprayed into the bed if the feed is sufficiently fluid. A less fluid feed such as, for example, one premixed with filler can be extruded into the bed. Many other methods of feed introduction are within the scope of this invention and the capability of those of ordinary skill in the art.
Particle form evaporation is not limited to any particular polymer and the scope of this invention should be interpreted accordingly. We note, however, that the process is especially well suited for the recovery of dry rubbery polymer such as, for example, styrene-butadiene copolymer from a rubbery polymer solution (as produced in a solution polymerization process) or from a rubbery polymer-containing latex (as produced in an emulsion polymerization process).
A problem encountered in the practice of the particle form evaporation process is that of start-up. Without a bed of hot agitated particles ready to receive the feed, the feed builds up in the system without adequate evaporation of solvent or liquid.